One of the greatest challenges found in the Oil and Gas Industry, is related to mitigation, treatment and remediation of hydrates.
Gas hydrates are crystalline solids based on water physically similar to ice, wherein small non-polarized molecules are captured inside “cages” of water molecules joined by hydrogen bonding. In other words, water acts as a host molecule and the host molecule is typically a gas.
Most part of gases with low molecular weight, as for example, O2, H2, N2, CO2, CH4, H2S, Ar, Kr, and Xe, as well as some upper hydrocarbons and freons may form hydrates under suitable conditions of temperature and pressure.
Formation and dissociation of hydrates occur through transitions of first order phase, and non-chemical reactions. However, once there is no binding between water molecules and gas at issue, hydrates may not be considered chemical compounds.
When hydrates' formation occurs in a flowing system, a blocking “plug” is formed avoiding the production flow. Such blocking is extremely difficult to be reverted and mechanisms normally employed for treating and dissociating hydrates and, consequently, the system unblocking, require several equipments and may take, eventually weeks, generating huge losses and increasing the risks involved in the process, besides the time wherein the production is stopped.
In this way, systems are operated with preventive measures in a way to avoid creating conditions favorable to hydrates formation. An example widely used in the systems is the injection of an alcohol, as for example, the monoethylene glycol (MEG), enabling the temperature of hydrate formation is displaced to a much lower temperature, even when pressure and temperature conditions are kept, eventually, enabling the production continuity.
Once formed, so that hydrates are dissociated it is necessary to make its phase change, modifying pressure or temperature variables, or even both. However, these modifications are only possible using the equipments specific for pressure relief, and may require the use of support vessels, fluids circulation, among others, impacting in the production and in the process cost.
Techniques used for heating submarine equipments externally through hot water circulation or even circulation of electrical current for remediation and treatment hydrate aiming its effective spreading, are known. However, it is not described any method or system involving the heat application internally to submarine equipment.
The U.S. Pat. No. 6,564,011 discloses a heating system, for remedying hydrate, applicable to submarine equipments for producing oil and gas, which is constituted of an electrical cable positioned in the external wall of the equipment, protected by a thermal isolating layer, and that generates heat by circulating electrical current.
The U.S. Pat. No. 5,424,608 discloses a heating system, for remedying hydrate, applicable to submarine equipments for producing oil and gas, which is constituted of a tubing positioned in the equipment external wall, protected by a thermal isolating layer, and that generates heat by circulating hot water.
In both documents systems applicable to submarine equipments are described. But, both use heat sources positioned in the external walls of these equipments.
Further, the use of heat sources outside the equipment, either in the case of electrical current circulation as in hot water circulation, it is not a much efficient feature. The heat transmission of the external part to the internal part may not occur in the most suitable manner, as well as the thermal coupling of the external wall of the equipment to its inside may not be good. In addition, the system assemble allows a lot of heat exchange with the external mean even in the presence of thermal insulation.
Due to lack of efficiency of the systems now existent, the amount of energy required for heating is too increased. Normally, for these cases the only source able to provide energy necessary for the system is found in the surface, once, difficultly a ROV have this energy amount available, which increase the cost and operationally makes it much harder for the systems using these solutions.
In this way, it is necessary to develop new alternative methods and systems most viable and efficient in the remediation and treatment of hydrate aiming its effective spreading, applicable to submarine equipments, promoting its unblocking, allowing its correct operation and enabling the production flow warranty.
Aiming to solve the state of art problems, mentioned above, it was developed a system able to generate and dissipate heat in the internal area of the equipment, using the electrical supply energy of a ROV.